1. Field of the Invention
The present invention relates to a pump for sucking and discharging fluid, to a sucking device for recovering liquid ejection equipped with the pump to keep a good ejection status and to an image forming apparatus equipped with the pump, particularly suitable for an ink-jet printer equipped with a plurality of eject heads.
2. Brief Description of the Related Art
The ink-jet printing is a method where an image is formed on a printing medium by ejecting tiny liquid droplets from eject ports of the ink-jet head and depositing them on the medium. In this kind of ink-jet head it is difficult to keep smooth ejection or impossible to eject the liquid due to clogging caused by liquid thickening as a result of drying liquid in liquid paths, by tiny foreign particles stuck to eject ports or by bubbles generated in ink in liquid paths.
As measures recovering such poor ejection status in the ink-jet head, a sucking method to remove thickened ink or bubbles in liquid paths from eject ports by reducing a pressure in liquid head with the aid of a pump is usually used. As the pump for the sucking, a plunger pump where a piston moves reciprocatingly in a cylinder or a tube pump where a flexible tube is ironed by a roller attached to the periphery of a rotating rotor, is selected according to conditions such as spacing efficiency and costs etc.
In an ink-jet color printer where several color inks for forming color images are used, usually two or more ink-jet head are used for accommodating several color inks. A unit having corresponding number of pumps, that works simultaneously, to ink-jet heads or a unit with one pump that works according to a time shared schedule for each ink-jet head is known as a sucking device for recovering liquid ejection equipped in the ink-jet printer.
Rough structures of such conventional sucking devices for liquid recovery are illustrated in FIG. 9 and FIG. 10. The device in FIG. 9 has pumps corresponding numbers to ink-jet heads, while the device in FIG. 10 has one pump to a plurality of ink-jet heads (In FIG. 10 two heads are illustrated.)
In FIG. 9 two ink-jet heads 53 and 54 are mounted on a carriage 52 which moves reciprocatingly along a guide rod 51. At the home position of the carriage 52, a pair of cap members 57, 58 that cover eject ports (not shown in FIG. 9) are arranged respectively so as to face and to move backward/forward against eject surfaces 55, 56 where ejects ports are formed. Plunger pumps 61, 62 are respectively connected to cap members 57, 58 via sucking pipes 59, 60. During sucking operations for recovering liquid ejection, cap members are pressed to eject surfaces 55, 56 and plunger pumps 61, 62 are activated so as to suck thickened ink in ink-jet heads 53, 54 and then so as to discharge the sucked ink to a waste ink tank (not shown in FIG. 9) via discharging ports 63, 64.
In FIG. 10 at the home position of the carriage 52, a pair of cap members 57, 58 that cover eject ports (not shown in FIG. 10) are arranged respectively so as to face and to move backward/forward against eject surfaces 55, 56 where eject ports are formed. A plunger pump 61 is connected to a cap member 57 via a sucking pipe 59 while a cap member 58 covers an eject surface 56. During sucking operations for recovering liquid ejection cap members 57, 58 are pressed to eject surfaces 55, 56 and a plunger pump 61 is activated so as to suck thickened ink and the like in ink-jet heads 53 and then so as to discharge to a waste ink tank (not shown in FIG. 10) via a discharge port 63. Then cap members 57, 58 are removed from eject surfaces 55, 56 and the carriage 52 is transferred to a position where the eject surface 56 of the other ink-jet head 54 faces the cap member 57. Again the cap member 57 is pressed to the eject surface 56 and the plunger pump 61 is activated so as to suck thickened ink and the like in ink-Jet head 54 and then so as to discharge to the waste ink tank (not shown in FIG. 10) via the discharge port 63.
Since pumps such as 61, 62 and so forth corresponding numbers to ink-jet heads such as 53, 54 and so forth are required in the device shown in FIG. 9, namely corresponding numbers of comprising parts are required, it is inevitable to increase the production cost of the device. In addition, since space to accommodate respective pumps 61, 62 and so forth is required, the larger sized sucking device i.e. a larger sized casing for the ink-jet printer is inevitable, which also leads to a cost increase.
Though the above-mentioned problems are solved by the conventional sucking device for recovering liquid ejection shown in FIG. 10, another problem where operating efficiency of the printer is lowered due to increased duration for the sucking operations for recovering liquid ejection against respective ink-jet heads 53, 54, which are carried out on the time sharing schedule. A further problem, a complicated controlling procedure for the recovering operations is required, is caused, since ink volumes sucked from ink-jet heads 53, 54 by one pump 61 should be set respectively.
One of the objectives of the present invention is to provide a compact pump that sucks and discharges fluid with respective desired volumes simultaneously in a complicated system.
The other objective of the present invention is to provide a sucking device for recovering liquid ejection and an image forming apparatus equipped with the pump which keeps liquid ejected from liquid eject ports in good ejecting status.
A first embodiment is a pump comprising; at least one separating wall dividing an internal space of a cylinder into a plurality of fluid compartments with respect to a longitudinal direction of the cylinder, a plurality of discharging ports connected respectively to the fluid compartments at one side of the cylinder with respect to the longitudinal direction, a plurality of sucking ports connected respectively to the fluid compartments at other remaining side of the cylinder with respect to the longitudinal direction, a plurality of pistons accommodated in the respective fluid compartments so as to slide in the respective fluid compartments and to divide respectively the fluid compartments into two rooms and a piston rod for common use to the respective pistons passing through the separating wall to reciprocate the pistons in the fluid compartments respectively.
According to the present invention pistons in fluid compartments are respectively moved by one piston rod so that liquid in each fluid compartment is sucked via each sucking port and discharged via each discharging port in accordance with the reciprocating movements of the piston rod.
Further a plurality pairs of stoppers arranged on the piston rod so as to face each other at both sides of respective pistons to regulate slide movements of the pistons along the piston rod, connecting paths formed between the piston rod and stoppers for connecting two compartments and switching valves to shut connecting paths during the forward movements of the piston rod toward discharging ports and to open connecting paths during the backward movements of the piston rod toward sucking ports may be arranged in the pump according to the first embodiment.
Respectively different fluid volumes sucked via sucking ports and discharged via discharging ports in accordance with the reciprocating movements of the piston rod may be attained by arranging different effective cross sectional areas of respective fluid compartments.
A second embodiment the present invention is a sucking device for recovering liquid ejection to maintain good ejecting status of the liquid ejected from eject ports having a plurality of cap members covering the eject ports of a plurality of liquid eject heads to eject liquid respectively and a pump for sucking liquid from the eject ports via the cap members. where;
the pump has at least one separating wall dividing an internal space of a cylinder into a plurality of liquid compartments with respect to a longitudinal direction of the cylinder, a plurality of discharging ports connected respectively to the liquid compartments at one side of the cylinder with respect to the longitudinal direction, a plurality of sucking ports connected respectively to the liquid compartments at other remaining side of the cylinder with respect to the longitudinal direction and also connected to the cap members, at least two pistons accommodated in the respective liquid compartments so as to slide in the respective liquid compartments and to divide respectively the liquid compartments into two rooms and a piston rod for common use to at least the two pistons passing through the separating wall to reciprocate at least the two pistons in the liquid compartments respectively.
In the sucking device for recovering liquid ejection according to the second embodiment, further a plurality pairs of stoppers arranged on the piston rod so as to face each other at both sides of respective pistons to regulate slide movements of the pistons along the piston rod, connecting paths formed between the piston rod and stoppers to connect two compartments and switching valves to shut connecting paths during the forward movements of the piston rod toward discharging ports and to open connecting paths during the backward movements of the piston rod toward sucking ports may be arranged.
Respectively different liquid volumes sucked via sucking ports and discharged via discharging ports in accordance with the reciprocating movements of the piston rod may be attained by arranging different effective cross sectional areas of respective liquid compartments.
As the above-mentioned liquid, ink and/or treatment liquid to adjust printing property of ink ejected on a printing medium may be used.
One of a plurality of the liquid eject heads may be used only for black ink while remaining other heads may be used for a plurality of color inks except black ink. In this case sucked volume of the black ink should be set preferably less than accumulated sucked volumes of color inks.
A third embodiment according to the present invention is an image forming apparatus to maintain good ejecting status of the liquid ejected from eject ports having a portion to install a plurality of liquid eject heads to eject liquid onto a printing medium from respective eject ports so as to form image, a plurality of cap members covering the respective eject ports of liquid eject heads and a pump for sucking liquid from the eject ports via the cap members, where;
the pump has at least one separating wall dividing an internal space of a cylinder into a plurality of liquid compartments with respect to a longitudinal direction of the cylinder, a plurality of discharging ports connected respectively to the liquid compartments at one side of the cylinder with respect to the longitudinal direction and also connected to the cap members, a plurality of sucking ports connected respectively to the liquid compartments at other remaining side of the cylinder with respect to the longitudinal direction, at least two pistons accommodated in respective liquid compartments so as to slide in the respective liquid compartments and to divide respectively liquid compartments into two rooms and a piston rod for common use to at least the two pistons passing through the separating wall to reciprocate at least the two pistons in the liquid compartments respectively.
In the image forming apparatus according to the third embodiment, further at least two stoppers arranged on the piston rod so as to face each other at both sides of respective pistons to regulate slide movements of the piston along the piston rod, connecting paths formed between the piston rod and stoppers to connect two compartments and switching valves to shut connecting paths during the forward movements of the piston rod toward discharging ports and to open connecting paths during the backward movements of the piston rod toward sucking ports may be arranged.
Respectively different liquid volumes sucked via sucking ports and discharged via discharging ports in accordance with the reciprocating movements of the piston rod may be attained by arranging different effective cross sectional areas of respective liquid compartments.
As the above-mentioned liquid, ink and/or treatment liquid to adjust printing property of the ink ejected on a printing medium may be used.
One of a plurality of the liquid eject heads may be used only for black ink while remaining other heads may be used for a plurality of color inks except black. In this case sucked volume of the black ink should be set preferably less than accumulated sucked volumes of color inks.
The portion to install eject heads may have a carriage moving in a direction to cross a transferring direction of the printing medium onto which liquid is ejected from the liquid eject ports. In this case liquid eject heads may be mounted on the carriage demountably via a mounting/demounting means.
Further, the eject heads may have eject energy generating members to eject liquid from eject ports. In this case electro-thermal energy conversion elements to generate enough thermal energy to cause a film boiling in the liquid may be employed as the eject energy generating members.